Bev. J. F. Blake — The Llanheris Tlnconformity. 



219 



elsewhere, for, as desii'ed by my critics, good " distinctions between 

 the various conglomerates and grits " have already been drawn, 

 and in most cases, as here, can be easily recognized. 



I regard all this as very strong evidence that there are uncon- 

 formable deposits here, and cannot see how it can be affected either 

 for good or ill by anything that may be seen in the railway cutting. 

 Nevertheless it is satisfactory to show how the neighbouring ex- 

 posures can be explained in relation to our conclusions. Thus on 

 the north-west side of the grounds we find purple slate and ordinary 

 St. Ann's grit coming on again at a higher surface-level. This 

 I explain by the hypothesis of a fault which has let down the uncon- 

 formable deposits to a lower level than they originally occupied. But 

 to support this hypothesis we should be able to point out the fault 

 and show that it lets down something — we cannot reasonably expect 

 any particular kind of rock — on the S.E. side. Such a fault we 

 can point to : see Fig. 5. This suggests at least, by the anticlinal 



Fig. 5. — Fault seen in tlie Llanberis rail-^vay cutting, looking N.E. (1) Purple 

 slate, (2) green slate, (3) slickeusided fault, (4) conglomerate, (5) grit. 



structure on the left, that it is a down-throw on the right, and, as 

 it happens, on this side are rocks, conglomerate and grit, which, 

 from what we have observed above, could easily be brought here 

 by a slight fault. 



In reference to this my critics say : " Mr. Blake speaks of it 

 as a slight fault, but it is only so on his own hypothesis, and to 

 argue from that statement is reasoning in a circle." But 1 have not 

 argued from it at all. If I were to do so now it would be to say 

 that the hypothesis, that this conglomerate has been let down from 

 above by a slight fault and forms the continuation of similar rocks 

 near at hand, is a less wild one than that which supposes it to be 

 "faulted up from great depths," and so have no relation to the 

 neighbouring conglomerates. This last hypothesis is not even 

 suggested by anything that is seen on the ground. 



Before leaving this district 1 should point out that the map of 

 it given by my critics is inconsistent. They draw a fault by the 

 Tan-y-pant inlet, and make the succession on the two sides of it 

 different. On one side it is felsite, conglomerate, felsitic grit, grit 

 with argillite; on the other, felsitic grit, purple slate, con- 

 glomerate, grit with argillite. These two successions cannot both 

 be the true one. 



The Tramway Section and Y Bigl. 



I will not here, as I did at the reading of my paper, explain the 

 corrections 1 have been led by additional observations to make in 

 my own map, as they lead me further from my critics' views, but 

 will confine myself to their statements. 



